4 Pag., 2 Tabl., 1 Fig. The definitive version is available at: http://www.sciencedirect.com/science/journal/01761617

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dc.description.abstract

The effects of Zn excess on carboxylate metabolism were investigated in sugar beet (Beta vulgaris L.) plants
grown hydroponically in a growth chamber. Root extracts of plants grown with 50 or 100 M Zn in the
nutrient solution showed increases in several enzymatic activities related to organic acid metabolism,
including citrate synthase and phosphoenolpyruvate carboxylase, when compared to activities in control
root extracts. Root citric and malic acid concentrations increased in plants grown with 100 M Zn, but
not in plants grown with 50 M Zn. In the xylem sap, plants grown with 50 and 100 M Zn showed
increases in the concentrations of citrate and malate compared to the controls. Leaves of plants grown
with 50 or 100 MZn showed increases in the concentrations of citric and malic acid and in the activities
of citrate synthase and fumarase. Leaf isocitrate dehydrogenase increased only in plants grown with
50 M Zn when compared to the controls. In plants grown with 300 M Zn, the only enzyme showing
activity increases in root extracts was citrate synthase, whereas the activities of other enzymes decreased
compared to the controls, and root citrate concentrations increased. In the 300 MZn-grown plants, the
xylem concentrations of citric and malic acids were higher than those of controls, whereas in leaf extracts
the activity of fumarase increased markedly, and the leaf citric acid concentration was higher than in the
controls. Based on our data, a metabolic model of the carboxylate metabolism in sugar beet plants grown
under Zn excess is proposed.

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dc.description.sponsorship

This work was supported by the Spanish Ministry of Science
and Innovation (grant AGL2007-61948, co-financed with FEDER)
and the Aragón Government (group A03). The HPLC–TOFMS apparatus
was co-financed with FEDER. R.S. and R.R-A were supported
by I3P-CSIC and FPI-MCINN pre-doctoral fellowships, respectively.